Regex Tester
Guide & Explanations
Online Regex Tester — JavaScript Regular Expression Debugger
The Regex Tester is an essential development tool for designing, testing, and validating JavaScript regular expressions. With an intuitive interface, it allows you to instantly visualize how your patterns interact with your data.
Why use a Regex Tester?
Regular expressions are powerful but complex. A small mistake in a capture group or a flag can make the pattern ineffective or even dangerous (e.g., ReDoS). Our tool lets you see matches in real-time, check the content of each capture group, and test your replacements (substitutions) before implementing them in your code.
Advanced Features
- Syntax Highlighting: Visualize your capture groups with distinct colors for easier reading.
- JS Flag Support: Manage Global (g), Case Insensitive (i), Multiline (m), dotAll (s), Unicode (u), and Sticky (y) flags.
- Substitution Module: Test your replacements using capture variables like
$1,$2, etc. - Detailed Analysis: A complete list of matches with start index and length for each found segment.
- Premium Ergonomics: Responsive interface, native dark mode, and synchronized scrolling between text and highlights.
Security and Performance
The tool uses your browser's native Regex engine. All processing is performed locally on your machine; your texts and patterns are never sent to any third-party server.
Frequently Asked Questions
Q: Is Regex Tester free to use?
R: Yes, the Regex Tester utility is 100% free. All tools on Dolf.in are accessible at no cost and without intrusive ads.
Q: Is my data secure?
R: Absolutely. Dolf.in uses a 'Serverless' approach: your data is processed locally in your browser and is never sent to our servers.
Q: Do I need to install any software?
R: No, no download or installation is required. Everything works directly in your web browser.